Transaction accelerator for client-server communication systems

ABSTRACT

In a network having transaction acceleration, for an accelerated transaction, a client directs a request to a client-side transaction handler that forwards the request to a server-side transaction handler, which in turn provides the request, or a representation thereof, to a server for responding to the request. The server sends the response to the server-side transaction handler, which forwards the response to the client-side transaction handler, which in turn provides the response to the client. Transactions are accelerated by the transaction handlers by storing segments of data used in the transactions in persistent segment storage accessible to the server-side transaction handler and in persistent segment storage accessible to the client-side transaction handler. When data is to be sent between the transaction handlers, the sending transaction handler compares the segments of the data to be sent with segments stored in its persistent segment storage and replaces segments of data with references to entries in its persistent segment storage that match or closely match the segments of data to be replaced. The receiving transaction store reconstructs the data sent by replacing segment references with corresponding segment data from its persistent segment storage, requesting missing segments from the sender as needed. The transaction accelerators could handle multiple clients and/or multiple servers and the segments stored in the persistent segment stores can relate to different transactions, different clients and/or different servers. Persistent segment stores can be prepopulated with segment data from other transaction accelerators.

CROSS-REFERENCES TO RELATED APPLICATIONS

U.S. patent application Ser. No. 10/285,330 entitled “Content-BasedSegmentation Scheme for Data Compression in Storage and TransmissionIncluding Hierarchical Segment Representation” [Attorney Docket No:021647-000200US] (hereinafter “McCanne II”) was filed of even date withthis application and is incorporated by reference herein for allpurposes.

BACKGROUND OF THE INVENTION

The present invention relates generally to systems for moving datathrough limited bandwidth channels efficiently and more particularly tohaving data available in response to a request for data over a limitedchannel faster than if the data were sent unprocessed in response to therequest.

Many applications and systems that operate well over high-speedconnections need to be adapted to run on slower speed connections. Forexample, operating a file system over a local area network (LAN) workswell, but often files need to be accessed where a high-speed link, suchas a LAN, is not available along the entire path from the client needingaccess to the file and the file server serving the file. Similar designproblems exist for other network services, such as e-mail services,computational services, multimedia, video conferencing, databasequerying, office collaboration, etc.

In a networked file system, for example, files used by applications inone place might be stored in another place. In a typical scenario, anumber of users operating at computers networked throughout anorganization and/or a geographic region share a file or sets of filesthat are stored in a file system. The file system might be near one ofthe users, but typically it is remote from most of the users, but theusers often expect the files to appear to be near their sites.

As used herein, “client” generally refers to a computer, computingdevice, peripheral, electronics, or the like, that makes a request fordata or an action, while “server” generally refers to a computer,computing device, peripheral, electronics, or the like, that operates inresponse to requests for data or action made by one or more clients.

A request can be for operation of the computer, computing device,peripheral, electronics, or the like, and/or for an application beingexecuted or controlled by the client. One example is a computer runninga word processing program that needs a document stored externally to thecomputer and uses a network file system client to make a request over anetwork to a file server. Another example is a request for an actiondirected at a server that itself performs the action, such as a printserver, a processing server, a control server, an equipment interfaceserver, and I/O (input/output) server, etc.

A request is often satisfied by a response message supplying the datarequested or performing the action requested, or a response messageindicating an inability to service the request, such as an error messageor an alert to a monitoring system of a failed or improper request. Aserver might also block a request, forward a request, transform arequest, or the like, and then respond to the request or not respond tothe request.

In some instances, an object normally thought of as a server can act asa client and make requests and an object normally thought of as a clientcan act as a server and respond to requests. Furthermore, a singleobject might be both a server and a client, for other servers/clients orfor itself. For example, a desktop computer might be running a databaseclient and a user interface for the database client. If the desktopcomputer user manipulated the database client to cause it to make arequest for data, the database client would issue a request, presumablyto a database server. If the database server were running on the samedesktop computer, the desktop computer would be, in effect, making arequest to itself. It should be understood that, as used herein, clientsand servers are often distinct and separated by a network, physicaldistance, security measures and other barriers, but those are notrequired characteristics of clients and servers.

In some cases, clients and servers are not necessarily exclusive. Forexample, in a peer-to-peer network, one peer might a request of anotherpeer but might also serve responses to that peer. Therefore, it shouldbe understood that while the terms “client” and “server” are typicallyused herein as the actors making “requests” and providing “responses”,respectively, those elements might take on other roles not clearlydelineated by the client-server paradigm.

Generally, a request-response cycle can be referred to as a“transaction” and for a given transaction, some object (physical,logical and/or virtual) can be said to be the “client” for thattransaction and some other object (physical, logical and/or virtual) canbe said to be the “server” for that transaction.

Often client-server transactions flow directly between the client andthe server across a packet network, but in some environments thesetransactions can be intercepted and forwarded through transport-level orapplication-level devices called “proxies”. In this case, a proxy is theterminus for the client connection and initiates another connection tothe server on behalf of the client. Alternatively, the proxy connects toone or more other proxies that in turn connect to the server. Each proxymay forward, modify, or otherwise transform the transactions as theyflow from the client to the server and vice versa. Examples of proxiesinclude (1) Web proxies that enhance performance through caching orenhance security by controlling access to servers, (2) mail relays thatforward mail from a client to another mail server, (3) DNS relays thatcache DNS name resolutions, and so forth.

As used herein, the terms “near”, “far”, “local” and “remote” mightrefer to physical distance, but more typically they refer to effectivedistance. The effective distance between two computers, computingdevices, servers, clients, peripherals, etc. is, at least approximately,a measure of the difficulty of getting data between the two computers.For example, where file data is stored on a hard drive connecteddirectly to a computer processor using that file data, and theconnection is through a dedicated high-speed bus, the hard drive and thecomputer processor are effectively “near” each other, but where thetraffic between the hard drive and the computer processor is over a slowbus, with more intervening events possible to waylay the data, the harddrive and the computer processor are said to be farther apart.

Greater and lesser physical distances need not correspond with greaterand lesser effective distances. For example, a file server and a desktopcomputer separated by miles of high-quality and high-bandwidth fiberoptics might have a smaller effective distance compared with a fileserver and a desktop computer separated by a few feet and coupled via awireless connection in a noisy environment.

In general, where the effective distances are great, more effort isneeded to create the impression of a shorter effective distance. Muchhas been developed to create this impression. For example, when theeffective distance is increased due to limited bandwidth, thatlimitation can be ameliorated using compression or by caching.Compression is a process of representing a number of bits of data usingfewer bits and doing so in a way that the original bits or at least asufficient approximation of the original bits can be recovered from aninverse of the compression process in most cases. Caching is the processof storing previously transmitted results in the hopes that the userwill request the results again and receive a response more quickly fromthe cache than if the results had to come from the original provider.

Compression allows for more efficient use of a limited bandwidth andmight result in less latency, but in some cases, no latency improvementoccurs. Latency, with respect to client-server transactions, is ameasure of the delay between when a request for data is made and therequested data is received. In some cases, compression might add to thelatency, if time is needed to compress data after the request is madeand time is needed to decompress the data after it is received. This maybe able to be improved if the data can be compressed ahead of time,before the request is made, but that may not be feasible if the data isnot necessarily available ahead of time for compression, or if thevolume of data from which the request will be served is too largerelative to the amount of data likely to be used.

Caching also provides some help in reducing effective distance, but insome situations it does not help much. For example, where a singleprocessor is retrieving data from memory it controls and does so in arepetitive fashion, as might be the case when reading processorinstructions from memory, caching can greatly speed a processor's tasks.In a typical cache arrangement, a requestor requests data from somememory, device or the like and the results are provided to the requestorand stored in a cache having a faster response time than the originaldevice supplying the data. Then, when the requestor requests that dataagain, if it is still in the cache, the cache can return the data inresponse to the request before the original device could have returnedit and the request is satisfied that much sooner.

Caching has its difficulties, one of which is that the data might changeat the source and the cache would then be supplying “stale” data to therequester. This is the “cache consistency” problem. Another problem withcaching is that the original source of the data might want to trackusage of data and would not be aware of uses that were served from thecache as opposed to from the original source. For example, where a Webserver is remote from a number of computers running Web browsers thatare “pointed to” that Web server, the Web browsers might cache Web pagesfrom that site as they are viewed, to avoid delays that might occur indownloading the Web page again. While this would improve performance inmany cases, and reduce the load on the Web server, the Web serveroperator might try to track the total number of “page views” but wouldbe ignorant of those served by the cache. In some cases, an Internetservice provider might operate the cache remote from the browsers andprovide cached content for a large number of browsers, so a Web serveroperator might even miss unique users entirely.

Additionally, the mechanism underlying Web caching provides only a loosemodel for consistency between the origin data and the cached data.Generally, Web data is cached for a period of time based on heuristicsor hints in the transactions independent of changes to the origin data.This means that cached Web data can occasionally become inconsistentwith the origin server and such inconsistencies are simply tolerated byWeb site operators, service providers, and users as a reasonableperformance trade-off. Unfortunately, this model of loose consistency isentirely inappropriate for general client-server communication likenetworked file systems. When a client interacts with a file server, theconsistency model must be wholly correct and accurate to ensure properoperation of the application using the file system.

Some solutions to network responsiveness deal with the problem at thefile system or at network layers. One proposed solution is the use of alow-bandwidth network file system, such as that described inMuthitacharoen, A., et al., “A Low-Bandwidth Network File System”, inProceedings of the 18th ACM Symposium on Operating Systems Principles(SOSP '01), pp. 174-187 (Chateau Lake Louise, Banff, Canada, October2001) (in vol. 35, 5 of ACM SIGOPS Operating Systems Review, ACM Press).In that system, called LBFS, clients employ “whole file” caching wherebyupon a file open operation, the client fetches all the data in the filefrom the server, then operates on the locally cached copy of the filedata. If the client makes changes to the file, those changes arepropagated back to the server when the client closes the file. Tooptimize these transfers, LBFS replaces pieces of the file with hashes,and the recipient uses the hashes in conjunction with a local file storeto resolve the hashes to the original portions of the file. Such systemshave limitations in that they are tied to file systems and generallyrequire modification of the clients and servers between whichresponsiveness is to be improved. Furthermore, the hashing schemeoperates over blocks of relatively large (average) size, which workspoorly when files are subject to fine-grained changes over time.Finally, LBFS is by design intimately tied to a network file systemprotocol. It is not able to optimize or accelerate other types ofclient-server transactions, e.g., e-mail, Web, streaming media, and soforth.

Another proposed solution is suggested by Spring, N., et al., “AProtocol-Independent Technique for Eliminating Redundant NetworkTraffic”, in Proceedings of ACM SIGCOMM (August 2000). As described inthat reference, network packets that are similar to recently transmittedpackets can be reduced in size by identifying repeated strings andreplacing the repeated strings with tokens to be resolved from a sharedpacket cache at either end of a network link. This approach, whilebeneficial, has a number of shortcomings. Because it operates solely onindividual packets, the performance gains that accrue are limited by theratio of the packet payload size to the packet header (since the packetheader is generally not compressible using the described technique).Also, because the mechanism is implemented at the packet level, it onlyapplies to regions of the network where two ends of a communicating pathhave been configured with the device. This configuration can bedifficult to achieve, and may be impractical in certain environments.Also, by caching network packets using a relatively small memory-basedcache with a first-in first-out replacement policy (without the aid of,for instance, a large disk-based backing store), the efficacy of theapproach is limited to detecting and exploiting communicationredundancies that are fairly localized in time. Finally, because thisapproach has no ties into the applications or servers that generate the(redundant) network traffic, there is no ability to anticipate wheredata might be used and pre-stage that data in the far-end cacheproviding potential further acceleration and optimization of networktraffic.

In a business that spans operations over wide area networks, a number ofless than ideal patches have been done in response to the problemsdescribed above. For example, some businesses resort to buying more andmore bandwidth to keep responsiveness up. Individuals in theorganization will attempt local solutions by turning to ad hoc e-mailcollaboration (which might make one file more readily accessible by oneuser, but adds version control problems and adds to the overall networkload). Other attempts to solve the problem might involve manuallycreating copies of data to operate on or pushing read-only replicas toremote servers.

In view of the above problems and the limitations with existingsolutions, improvements can be made in how data is transported fortransactions over a network.

BRIEF SUMMARY OF THE INVENTION

In embodiments of a network having transaction acceleration, for anaccelerated transaction, a client directs a request to a client-sidetransaction handler that forwards the request to a server-sidetransaction handler, which in turn provides the request, or arepresentation thereof, to a server for responding to the request. Theserver sends the response to the server-side transaction handler, whichforwards the response to the client-side transaction handler, which inturn provides the response to the client. Transactions are acceleratedby the transaction handlers by storing segments of data used in thetransactions in persistent segment storage accessible to the server-sidetransaction handler and in persistent segment storage accessible to theclient-side transaction handler. When data is to be sent between thetransaction handlers, the sending transaction handler compares thesegments of the data to be sent with segments stored in its persistentsegment storage and replaces segments of data with references to entriesin its persistent segment storage that match or closely match thesegments of data to be replaced. The data to be sent might be sent froma client to a server, from a server to a client, from a peer to a peer,etc. The receiving transaction store then reconstructs the data sent byreplacing the segment references with corresponding segment data fromits persistent segment storage. If segments are referred to but do notexist in the receiver's persistent segment store, the receiver can issuerequests for the missing segments from the sender via a side channel orvia the link used to send the references to the segments. Where thepersistent segment storage at each end is populated with segments likelyto be repeated, such replacement of segments will occur often, resultingin much less bandwidth use over the network, thus acceleratingtransactions.

The transaction accelerators could be dedicated, such that theclient-side transaction accelerator interacts with only one client andthe server-side transaction accelerator interacts with only one server,but the transaction accelerators might also handle more than one clientand/or more than one server. Where multiple transactions are handled,either for the same clients and servers, or over possibly differentclients and possibly different servers, the segments stored in thepersistent segment stores can relate to different transactions,different clients and/or different servers. For example, if atransaction accelerator encounters a segment of data and stores it inits persistent segment store in handling a given transaction, areference to that segment of data might be used again in a differenttransaction, relating to a different client or the same client and adifferent server or the same server, or relating to an entirelydifferent client-server application.

In some embodiments, transaction accelerators' persistent segment storesare pre-populated with segment data from other transaction accelerators,so that when a transaction occurs, more segments are available at thesender end for replacement with references and more segments areavailable at the receiving end for reconstruction from the references.

Other features and advantages of the invention will be apparent in viewof the following detailed description and preferred embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a networked client-server system accordingto embodiments of the present invention.

FIG. 2 is a block diagram of the system of FIG. 1, showing a client-sidetransaction accelerator (“CTA”) and a server-side transactionaccelerator (“STA”) in greater detail and, for space considerations,showing less detail of the overall system.

FIG. 3 is an illustration of data organization in embodiments of apersistent segment store (“PSS”) as might be used with the system shownin FIG. 1.

FIG. 4 is a block diagram of an encoder as might be used in thetransaction transformers (“TT”) of FIG. 2.

FIG. 5 is a block diagram of a decoder as might be used in the inversetransaction transformers (“TT-1”) of FIG. 2.

FIG. 6 is an illustration of an encoding process wherein input data issegmented and represented by references to data segments.

FIG. 7 is a flowchart illustrating a process for decoding data as mightbe output by the encoder of FIG. 4.

FIG. 8 is a block diagram of a networked system wherein transactionacceleration is implemented and uses a proactive segment distributor(“PSD”).

FIG. 9 is a block diagram of a networked peer-to-peer system accordingto embodiments of the present invention.

FIG. 10 is a block diagram of a networked system wherein transactionacceleration is implemented and the client-side transaction acceleratoris integrated in with the client.

FIG. 11 is a block diagram of a networked system wherein transactionacceleration is implemented and the server-side transaction acceleratoris integrated in with the server.

FIG. 12 is a block diagram of a networked system wherein transactionacceleration is implemented and a PSS is shared among a plurality oftransaction accelerators.

FIG. 13 is a block diagram showing a multicast implementation of thesystem of FIG. 12, wherein multicast communications are used forupdating and reading a shared PSS.

FIG. 14 is a block diagram showing a multicast implementation of aplurality of clients coupled locally through a LAN and to a WAN.

FIG. 15 is a block diagram of a networked system wherein transactionacceleration is implemented and the network handles a variety ofprotocols and services.

DETAILED DESCRIPTION OF THE INVENTION

The present invention has many applications, as will be apparent afterreading this disclosure. In describing an embodiment of a transactionacceleration system according to the present invention, only a few ofthe possible variations are described. Other applications and variationswill be apparent to one of ordinary skill in the art, so the inventionshould not be construed as narrowly as the examples, but rather inaccordance with the appended claims.

A transaction, as the term is used herein, is a logical set of stepsthat result in data moving from one place to another. In some cases, thedata being moved exists at its origin independent of the transaction,such as a file read transaction where the file exists on the disk of theserver. In other cases, the data is generated for the transaction at theorigin, such as in response to a request for computation, lookup, etc.Typically, the computer, computer device, etc. initiating thetransaction is referred to as the “client” and the computer, computerdevice, etc. that responds, or is expected to respond, is referred to asthe “server”. Data can flow in either direction. For example, a filesystem client might initiate a transaction by requesting a file read.The corresponding data will be returned from the server responding tothe request, so in that case, the bulk of the data flows from the serverto the client. However, where a client initiates a file writetransaction, the bulk of the data flows from the client to the server,either as part of the initial request or as subsequent messages. Atransaction can be in multiple parts, but in a simple transaction, aclient sends a request (data, a message, a signal, etc., explicitlybeing the request or indicative of or representing of the request) to aserver and the server responds with a response (data, a message, asignal, etc., explicitly being the response or indicative of orrepresenting of the response) to the client. More complex transactions,for example, might involve some back and forth, as might be needed for aserver to clarify a request, verify the authority of the client toreceive a response to the request, get additional information needed forpreparing the response, etc.

Herein, the typical example of a connection between a client and aserver is a packet network, but other connection means can also be used,such as a point-to-point wired or wireless channel. These elements willbe generalized and referred to here as “nodes” with a channel assumedfor communication between the nodes.

A transaction might begin with a client at one node making a request forfile data directed to a server at another node, followed by a deliveryof a response containing the requested file data. Other transactionsmight be a request for a specific part of a file, all the file, all orsome of another data construct, or a transaction might relate to dataflowing from the requester or relate to a command. Examples oftransactions include “read a block”, “read a file”, “read a stream”,“write a block with this data” (an example of data flowing from therequester), “open a file”, “perform a calculation on this data”, “get ane-mail with these characteristics”, “send an e-mail”, “check for newemails”, “list directory contents”, etc.

Some transactions might involve large amounts of data flowing in onedirection or both directions. Some transactions might even involveinteractions having more than one requestor and/or more than onereceiver. For clarity of description, these many transaction types aredescribed in terms of a typical simple transaction, where one clientmakes a request of one server and that one server responds to therequest in a manner expected by the client. However, upon reading thisdisclosure, a person of ordinary skill will be able to apply theseconcepts to one-to-many and many-to-many transactions between client(s)and server(s) or more generally between two nodes. Where data flow isdescribed in one direction, it should be understood that data might flowin the other direction and/or information might flow in only onedirection, but data and/or signals flow in both directions to accomplishthe movement of information.

Using some of the systems described herein, client access to a server(and vice versa where needed), can be “tunneled” through transactionaccelerators that map transactions onto sequences of variable-lengthsegments with content-induced segment cut points. The segments can bestored at various places, typically within high-speed access of both theclients and the servers, with the segments stored using a scalable,persistent naming system. The segments can be decoupled from file-systemand other system data blocks and structures, so that a matching segmentmight be found in multiple contexts. Instead of caching files, blocks,or other system dependent constructs, segments can be stored and boundto references that are used to represent the segment contents.

FIG. 1 is a block diagram of a networked client-server system 10according to embodiments of the present invention, where suchtransactions might occur. As shown there, clients 12 are coupled toservers 14 over a network 16, via client-side transaction accelerators(“CTA's”) 20 and server-side transaction accelerators (“STA's”) 22.Where the location of a transaction accelerator is not specific, it isreferred to herein as a “TA”, indicating that it could be referring to aclient-side transaction accelerator, a server-side transactionaccelerator, a peer transaction accelerator, or possibly even atransaction accelerator that is used by clients and servers (andpossibly also peers).

Although not shown in FIG. 1, additional paths between clients andservers (also possibly between clients and clients and between serversand servers) might be present and bypass the TA's. Such additional pathscould be used to carry conventional traffic, such as transactions thatare not likely to benefit from transaction acceleration. By routing suchtransactions around the TA's, the state of the TA's can remain focusedon the accelerated transaction, for example, by not having thepersistent segment storage (described below) of a TA storing segmentsfrom transactions not likely to benefit from transaction acceleration.

As shown, a CTA 20 might serve one or more clients and multiple CTA's 20might be implemented on a network. As used herein and unless otherwiseindicated, the index “n” refers to an indefinite integer and eachdistinct use of the index might refer to a different indefinite integer.For example, FIG. 1 illustrates that there can be some number of CTA'sand some number of STA's and there need not be a one-to-onecorrespondence. In general, the number of CTA's might be based on thenumber of clients, number of expected clients, network layout, etc.,while the number of STA's might be based on the number of servers, thenumber of expected servers, network layout, etc. In someimplementations, each server connects to an STA dedicated to thatserver. In some implementations, a plurality of servers might be coupledto a server farm manager 24 and in turn coupled to Internet 16 via anSTA. In some cases, a client might interact with more than one CTA, asillustrated by line 27 in FIG. 1 and a server might interact with morethan one STA, as illustrated by line 29 in FIG. 1.

Where one CTA interacts with one STA and requests are received frommultiple clients connected to that CTA, the corresponding STA routeseach client request to the server(s) to which the request is directed.However, the TA's might be more closely coupled to theirclients/servers, such that all, or nearly all, accelerated transactionsfrom one client pass through that one client's CTA, and all, or nearlyall, accelerated transactions to one server, pass through that oneserver's STA. Additionally, in some implementations, TA's share state,so that transactions in one TA might benefit from segments stored atanother TA.

Client connections can be routed to a CTA in a number of ways, similarto how prior art proxies function with respect to clients. For example,redirection using the Domain Name System (DNS) can be used to cause aclient to resolve the IP address of the CTA instead of the server andthereby route requests to the CTA. Alternatively, the client or theclient's application could be statically configured to use a particularCTA or a set of CTA's on a per-application basis. Once the clientconnection arrives at a CTA, the CTA can then contact the appropriateSTA via a lookup process that could work in a number of ways. Forexample a mapping table (maintained on a centralized and query-abledatabase or configured into the CTA) could be used to direct the CTA tothe appropriate STA; or information conveyed in the transaction couldallow the CTA to discover which STA to use; or configurable policiescould be programmed into the CTA indicating which transport ports shouldbe relayed to which STA's. Likewise, the STA could use similar lookupprocesses to decide which server to contact for a new client connectionarriving from a CTA. The STA could also use data in the transactions toinfer what server to connect to (e.g., an HTTP Web request contains theserver's identity, as does a connection setup request for a CIFS fileserver connection).

It should be understood that while the network shown in FIG. 1 is theInternet, a global internetwork of networks in common use today, othernetworks can be substituted therefor. For example, network traffic overthe Internet can travel through public networks and is largely based onTCP/IP (Transmission Control Protocol/Internet Protocol) packetswitching. However, the embodiments of the invention shown herein mightalso be used on networks that are not public, such as intranets,extranets, and virtual private networks. The embodiments might also beused with WAN's, LAN's, WAN/LAN couplings, wireless connections, mobilelinks, satellite links, cellular telephone networks, or any othernetwork where responsiveness is a concern. In addition, while TCP/IP isthe most common packet switched protocol today and thus serves as a goodexample, other network protocols might be used (Ethernet, etc.). As foroverlying protocols, the clients and servers described herein (andpeers, as described below) might use HTTP, FTP, SNMP, POP3, IMAP, SMTP,NFS, CIFS, RPC, or other open or proprietary protocols for transport ofdata.

In a common transaction, a client sends a request for a file, data blockor other unit of data to a server and the server responds with dataresponsive to the request, if possible. For example, where the client isa computer running a computer-aided design (CAD) program and needs a CADfile stored on a file server, the client might formulate a request forthe file, encapsulate the request as a message and send that messageover the network to the appropriate file server. The file server mightthen perform authentication, check for the existence of the file at thefile server and, if the client is authorized to have the file and thefile exists, the file server might create a message or a set of messagesor packets containing the data of the file requested and send thosemessages/packets to the client that made the request.

Using TA's might improve the responsiveness of the transaction, i.e.,accelerate the transaction. In a typical environment, the links 27between clients and CTA's are fast links, such as local area network(LAN) links and the links over network 16 are slower in terms of latencyand bandwidth. “Latency” refers to the time between when a message issent and when it is received (usually measured in time units) and“bandwidth” refers to how much capacity (usually measured in number ofbits per unit time) can be carried over a link for a particular task. Inmany cases, low bandwidth might result in high latency, but thosefactors can be independent such that it is possible to have highbandwidth but still have high latency. Other factors might affectresponsiveness and/or bandwidth cost, such as the reliability of thelink and bandwidth usage.

In a typical file request transaction using the TA's, a client 12initiates a transaction with a server 14 by sending a request message.As explained above, if the transaction involves a small number of bitsor other factors exist, using TA's might not get the transaction doneany faster and thus the transaction might go over a conventional packetpath. However, the transaction might go through the TA's anyway, whichmight be useful, as explained below, so that the TA's have a morecomplete view of the traffic. As one example, if a client request passesthrough the CTA, the CTA can remember the request and match up theresponse to the request to provide additional services to the client.The CTA might also use the requests to guess at what future events mightbe and use those guesses to further optimize the transactionacceleration process.

When a server 14 receives a request, it formulates a response to therequest, and sends it towards the client via the STA 22 to which it iscoupled. In a basic implementation, each client is coupled to one CTAand each server is coupled to one STA, but in more compleximplementations, a server might be coupled to more than one STA and usesome optimization logic to determine which STA to use at which time. Aclient might be coupled to more than one CTA and use some optimizationlogic to determine which CTA to use at which time.

The CTA 20 could send the request to the appropriate STA 22 unchangedand/or the receiving STA 22 could receive the response from a server andsend the response to the appropriate CTA 20 unchanged. However, wherethe request or the response comprises a large amount of data,significant transaction acceleration might be expected in such instancesif the data is “compressed” as described herein by storing segments ofdata at the receiving end and replacing data at the sending end withreference to the stored segments. In some cases, such substitution doesnot accelerate a transaction, but might still have benefits, such as“priming the pump” with data, so that the receiving ends have segmentdata that can be used later in reconstructing transmitted data thatreferences those segments. Such concepts are more clearly described withreference to FIG. 2.

As will be shown in FIG. 2 and other figures in more detail, transactionrequests and responses are routed through TA's instead of going directlyfrom a client to a server. Of course, in some configurations, a CTA andclient and/or an STA and server are tightly integrated such that anexplicit rerouting is not required. Nonetheless, it is useful to assumethat the data is routed, at least because it clarifies that traffic froma client can route through a CTA and traffic from a server can routethrough an STA, but traffic can also bypass the TA's. Since the TA's canoperate at the transport network level, they can operate on transactionsas the unit of work.

One configuration for easily routing traffic to be accelerated is viathe use of connection proxies. Thus, a CTA would serve as a connectionproxy for the server with which a client is entering into a transactionand the STA would serve as a connection proxy for the client to whichthe server is responding. It should be understood that a TA system couldbe implemented with symmetric TA's, e.g., where a CTA and an STA arearranged to be substantially similar except possibly that the CTA is setup to expect to encounter new transactions from a client, but not froman STA and an STA is set up to not expect to encounter new transactionsfrom a server, but to expect them from a CTA.

FIG. 2 is a block diagram of portions of system 10, showing a CTA 20, anSTA 22 and their interconnections in greater detail. While only oneclient and one server are shown, it should be understood that thevarious elements of FIG. 1 might also be present, even if not shown. Forexample, CTA 20 might be handling transactions from more than one clientand STA 22 might be handling transactions with more than one server. Asillustrated there in FIG. 2, client 12 is coupled to a client proxy 30of CTA 20. While other forms of multiplexing and de-multiplexing trafficto and from clients could be used, in this example, a client proxy isused to receive data for CTA 20 from one or more clients and to senddata for the CTA 20 to the one or more clients. The other elements ofCTA 20 shown in FIG. 2 include a transaction transformer (TT) 32, aninverse transaction transformer (TT⁻¹) 34, a persistent segment store(PSS) 36 and a reference resolver (RR) 38. Server 14 is coupled to aserver proxy 40 of STA 22, which is shown including elements similar tothose of CTA 20, such as a transaction transformer (TT) 42, an inversetransaction transformer (TT⁻¹) 44, a persistent segment store (PSS) 46and a reference resolver (RR) 48.

Client 12 is coupled to client proxy 30, which is coupled to TT 32 andTT⁻¹ 34. TT 32 is coupled to PSS 36 and to the network between CTA 20and STA 22. TT⁻¹ 34 is coupled to PSS 36, client proxy 30, RR 38 and tothe network between CTA 20 and STA 22. RR 38, as shown, is also coupledto PSS 36 and to the network between CTA 20 and STA 22.

On the other side of the figure, server 14 is coupled to server proxy40, which is coupled to TT 42 and TT⁻¹ 44. TT 42 is coupled to PSS 46and to the network between STA 22 and CTA 20. TT⁻¹ 44 is coupled to PSS46, server proxy 40, RR 48 and to the network between STA 22 and CTA 20.RR 48, as shown, is also coupled to PSS 46 and to the network betweenSTA 22 and CTA 20.

It should be understood that some or all of the elements of CTA 20and/or STA 22 may be integrated within CTA 20 or STA 22, such thatexplicit connections between the elements are not needed, but a logicalcoupling would still exist. For example, CTA 20 might be implementedentirely as a single program with data memory, program memory and aprocessor, with the program memory containing instructions forimplementing the client proxy, the TT, the TT⁻¹ and the RR, when suchinstructions are executed by the processor. In such an implementation,the data memory could be logically partitioned to hold variables neededfor the processor execution of the instructions, state of the clientproxy, TT, TT⁻¹ and RR, as well as the contents of the PSS. The samecould be true of STA 22.

The PSS can be a disk subsystem, a memory subsystem, or portionsthereof. The PSS can also be a memory subsystem with disk backing store,a database server, a database, etc.

Of the connections shown, arrows indicate the most common direction ordirections of flow of information, but information could flow inadditional directions and information flow in a single direction mightinvolve data flowing in the reverse direction as well. For example, TT32 generally sends information in the direction of TT⁻¹ 44, but datasuch as confirmations, handshakes, etc., may flow from TT⁻¹ 44 to TT 32.

Some of the connections are shown as dotted lines spanning between CTA20 and STA 22 (e.g., between the TT's and TT⁻¹'s and the RR's). Althoughthey are shown by separate lines, it should be understood that theselines can represent distinct network connections, or separate packetflows over a common network connection, or even shared packets among thelogical connection shown. Thus, dotted line connections might beindependent connections comprising more than one port number and/or morethan one IP address, but they might also be three logical connectionsover one packet-switched connection, such as via a common path usingcommon port numbers and common IP addresses.

The undotted lines between the client and the CTA and the server and STAare labeled as “LAN/direct” to indicate that those connections arelikely higher performance (latency, bandwidth, reliability, etc.) thanthe connections between the TA's labeled “Internet/WAN/etc.” Examples ofthe former include LANs, cables, motherboards, CPU busses, etc. Thesystem is still operable if the connections between the TA's are higherperformance connections, but some of the benefits of transactionacceleration might not be seen.

In operation, the CTA's and STA's examine the payloads of theirtransactions where warranted and store/cache strings or other sequencesof data (“segments”) derived from those payloads using a unique namingscheme that can be independent of the transaction. When sending thepayload from one TA to another, the TA may replace the segment data withreferences to the segment data. One indication that this replacementshould occur is when the segment data is such that the sender can expectthat the receiver would have that uniquely named segment data, eitherbecause it appeared in an earlier transaction or was sent through otherprocesses to the receiver, however other indications or no indicationmay be used to determine whether or not to replace the segment data witha reference. In some cases segmentation and substitution will not beperformed where acceleration is not expected, such as where the amountof data involved is small. The segmented portions of the transaction canbe any portion of the data sent, so long as the transaction is stillidentifiable at the receiving end enough to be reconstructed.

Because the segments can be uniquely named and the names can beindependent of the transaction, a segment appearing in one transactioncan be stored at both TA's and used for accelerating other transactions.For example, where a client initiates a number of file requesttransactions, if the files have data in common, that common data mightbe formed as a segment and after the first such segment is transmitted,all further requests for files with the common data would have a segmentreference substituted for the common data, to be replaced by the CTAbefore sending the reconstructed file to the client making the request.Similarly, where one CTA handles more than one client, the segments forone client can be used for another client.

Where the transactions are other than file transactions, analogousacceleration is possible. For example, where a CTA is coupled to ane-mail client and an STA is coupled to an e-mail server, an e-mailattachment that many clients are requesting via the CTA can berepresented as a segment after the CTA has obtained the contents of theattachment and then each subsequent time a client requests theattachment, the responding STA will replace the attachment with thesegment reference and the receiving CTA will replace the reference withthe stored attachment. Since the attachment is stored as a segmentindependent of the transaction, the same segment data might be found ina file transaction, additional e-mail transactions or othertransactions, and in each case, the sender replaces the data with thesegment reference and the receiver replaces the segment reference withthe segment data.

Note that there are several advantages of such an approach. Unlikecaching, where a transaction result is cached and reused when thattransaction is repeated and the cache is not invalidated, a segment canbe used in several unrelated transactions and segments need not bebounded at arbitrary cut points. Since segment names and content can beindependent of any particular bit stream or transaction, they cansurvive in the persistent storage for arbitrary amounts of time, even ifsystem components crash and reboot, new components are added into themix, the segment store is erased, etc.

The receiver can obtain the segment data for inclusion in its persistentstore and/or for decoding before, during or after receiving thetransmission of a sequence of references from the sender. Preferably,the segment data is obtained in ways that improve the responsiveness ofthe transaction, when possible. For example, if a need for a segment canbe anticipated, the segment data can be sent before it is needed, sothat when it is needed, it can be obtained faster. However, in somecases, such as where a receiving TA does not have any stored segmentsand has to obtain all of them during the transaction, transactionacceleration might not occur since the total amount of data that needsto be sent is not reduced.

Assuming a request flows through the TA's, client 12 would send therequest to client proxy 30, which would then send it to TT 32, eithermodifying the request or merely forwarding it. TT 32 determines how totransform the request, storing segments and references thereto in PSS 36as needed (explained in more detail below), and sends the transformed orunmodified request to TT⁻¹ 44, which performs any needed inversetransformations (explained in more detail below) and sends the requestto server proxy 40, and in turn to server 14. An analogous path is takenfor the response.

Where a message (such as a client request message or a server responsemessage) has been transformed, the inverse transaction transformer usesthe contents of its PSS to reconstruct the message. In a simple case,the TT for a sender (client or server) transforms a message byidentifying segments of the message, replacing identified segments withreferences and storing the reference-segment pairs in the PSS. Sometechniques for intelligently segmenting data based on content aredescribed in McCanne II. By sending references instead of segment data,the total traffic between TA's during the transaction is reduced, orperhaps the bulk of the traffic is moved to a less critical time or lesscritical path.

Where the receiving TA has in its PSS the reference-segment pairs usedby the sending TT, the receiving TT⁻¹ can regenerate the sent data byreplacing the references with their corresponding segment data. Thereceiving TA can obtain segment data for storage in its PSS from a sidechannel or as part of the traffic from the sending TA. Thus, the datatransmitted from the sending TA to the receiving TA may include bothreferences to segments and also “bindings” representing the mapping froma reference to the segment data. Of course, if each time a segment isreplaced with a reference and both the reference and the binding aresent, not much bandwidth will be saved, and in fact the bandwidth willbe increased. However, where the sender suspects the receiver alreadyhas the binding, the sender can omit the bindings, resulting insubstantially less traffic. Note that exact knowledge of what thereceiver has is not required to achieve the benefits from this process.

In some cases, all of the data needed to fulfill a request is present atthe client's PSS, so that if a caching scheme were used instead, withthe PSS as the cache, no message would need to be sent to the server atall. However, this would require that the CTA be sufficientlyintelligent enough to understand the client transaction and construct aproper response from the data that is present in the PSS. This is adifficult problem in general, especially when many different applicationtypes and client-server scenarios are proxied through the CTA andcertain client-server interactions simply are not amenable to caching(e.g., file system write operations, database update transactions, filedeletion, etc). Thus, it is preferable to use the TA's described hereand for the messages to be sent to the server anyway, so that theinconsistencies of caching schemes can be avoided. For example, if afile server receives all the requests for a file, even if the entirefile content is present at the client, the server can track requests andthe server can implement complex operations such as file lockingprotocols even though no substantial file data need be transmittedacross the network.

In preferred embodiments of the TA system, the above benefits accrueautomatically. For example, the STA segments each transaction payloadand replaces segments with references. For the segment data the STAsuspects the CTA has, the STA uses the references that it knows the CTAhas for those segments. When data changes at the server, rather than tryto modify the existing segments in the PSS, the STA creates new segmentsrepresenting the changed data and can assume that the CTA does not havethose segments. In this case, the STA uses new references to the newsegments representing the changed data. At the receiving TA (the CTA, inthis example), the references to older data might be resolved frombindings stored in the receiver's PSS, but for the new, changedsegments, the references are resolved from bindings included in thestream from the sender. Those bindings can then be stored by thereceiver's TT⁻¹ into the receiver's PSS, so that they are available forlater transformations by that receiver.

In addition, because references are globally unique (as describedbelow), they can be used by any TA in the network, not just the STA andCTA pair as described in this example. For example, the CTA mightcommunicate with a different STA and use a reference allocated by theformer STA. If the two STA's communicate in the future, they immediatelyenjoy the benefit of the segment binding that has been disseminated toboth devices.

Several schemes are usable to ensure that each named segment has aunique name throughout the system at any given time (i.e., that no twosegments with different data are erroneously assigned the same name). Inone approach, every segment reference is generated as a large randomnumber, where the number of unique references is much lower than thespace of all possible large random numbers. This scheme is less thandesirable because a small possibility exists that two segments will havethe same segment reference but different segment data, which would causea receiving TA to erroneously reconstruct a message with the wrong data.

Another scheme is to generate hashes from the segment data so that eachsegment reference is a hash of the segment data and different segmentdata will result in different hashes, except in very rare cases. Yetagain, the rare cases will always be problematic, as long as twodegenerate segments with the same reference but different segment dataexist in the system. Unlike the random number case, this problem willrecur every time that particular data pattern exists in the data stream.

One simple approach that avoids the above problems is for each sendingTA to generate a segment reference from the combination of a unique ID(such as the host IP address, when globally unique IP addresses are usedthroughout the network, the host MAC address, an assigned uniqueidentifier, or other means) and a sequential number. In mostimplementations, the maximum number of unique sequential numbers isbounded, and thus will eventually need to be reused. However, a namespace can be made effectively unbounded by using a large enough labelnumber space that the supply could last millions of years and no specialhandling would be needed. The large labels could be compressed toprovide for small footprints for the labels.

Since labels will be allocated sequentially and because thecorresponding segments will often appear in the same sequence, very goodcompression of the labels can be achieved in practice (not just acrossthe network but also in the data structures that represent strings oflabels that are invariably employed throughout the system). Additionalcompression is also possible on the sending TA's output stream. Forexample, where the receiving TA can identify the sending TA and thesending TA's references include the sending TA's unique ID, that ID neednot appear in the sent data, as the receiving TA would know what ID touse in forming the references (although, in general, extra informationmust be communicated when a sending TA references not just its ownbindings but bindings and labels that originate from other TA's). Oneother advantage of this approach is that a TA can identify the source ofeach of the segments in its PSS from the ID component of the segmentreference, for use in statistical analysis, diagnostics, and the like.

In a system where the labels are intended to be reused during theexpected lifetime of the system, the system preferably includes amechanism to “expire” a reference binding, with this expiration beingpropagated to all TA's in a network. One approach is to timestamp eachsegment, so that it has a fixed lifetime that can easily be inferred byeach component in the system that uses the segment. If time stamps areassigned to labels in a coarse-grained fashion (e.g., the timestampchanges just once a day), then label compression eliminates most of theprotocol header associated with assigning and communicating timestamps.A TA can thereby infer when it is safe to reuse a particular set oflabels.

Yet another alternative for managing the segment name space is to havecentral allocation of unique references. In such cases, a sending TAwould request a reference, or a block of references, from a source thatguarantees that the references are unique. In addition, each allocationcould be assigned a maximum time-to-live so that the allocation ofreferences, or blocks of references, could be implicitly reused.

It may happen that a sending TA assumes a certain binding is present ata receiving TA when it is not. This might occur where the receiving TAhas a PSS overflow, corruption, loss of power, etc., or the receiving TAintentionally removed the binding. In such cases, the receiving TA canobtain the segment data without aborting or having to report thetransaction as a failure. This allows the system to gracefully deal withmissing data due to a disk getting full, disk failure, network failure,system crash, etc. If a sending TA assumes that a receiving TA has abinding, the sending TA will send a message using that binding'sreference, but will not include the segment data of the binding. Whenthe receiving TT⁻¹ tries to resolve the reference, it will fail. Inthose cases, the receiving TT⁻¹ sends a resolution request to its RR,which then makes a request to the sender's RR. The TT⁻¹ can just blockand restart when the needed data is received, perhaps due to an eventtrigger signaling that the data is available; this process could betransparent to the TT⁻¹ (other than a delay in getting a response). Oncethe segment data is received at the receiver, the receiver's RR caneither provide the data to the receiver's TT⁻¹ or just put it in thereceiver's PSS, where it can be accessed by the receiver's TT⁻¹. As thesender's TT adds bindings to its PSS as appropriate, it maintains thosebindings for a guaranteed minimum amount of time; as such when it isreplacing segment data with references, it can be guaranteed that whenthe receiver's RR makes a request of the sender's RR for that segmentdata, it will be present in the sender's PSS, provided the guaranteed“lifetime” of a segment at the sender is greater than the maximum amountof time the receiver might require to make a segment request.

FIG. 3 contains an illustration of data organization of a bindings tableof a simple PSS. As shown there, the bindings table stores a pluralityof bindings, such as (R₁,S₁), (R₂,S₂), etc., where R_(i) is thereference label for the i-th binding and S_(i) is the segment data forthe i-th binding. A timestamp for each binding might be used for agingthe bindings. The binding records might include other fields not shownin FIG. 3, such as those listed in Table 1 and/or similar or additionalfields, possibly in addition to other tables, data structures, objectsand/or code. TABLE 1. TABLE 1 number of times accessed last access timelast modify time lifetime encoding method identifier (e.g., unencodedraw data, run-length encoded, MD5 encoded, encrypted) fingerprint errorcorrection data (if not interspersed with segment data) indication ofthe sender that created the binding (the binding “owner”) creation time(useful for timing out segments, such as by using the lifetime field)other fields

Some additional data structures might include an index of references, anindex of other fields, an index of segments, etc., for searching orotherwise processing the contents of the PSS. Segments could be indexedin many ways that could be useful for the encoding process, but oneembodiment builds an index of segments where a well-known hash, computedover all of the data that comprises the segment, is used as the key. Ifthe encoding method identifier is used, segment data can be encoded forerror correction, encryption, etc.

For some segment data, it might be suitable to compress the segment datato reduce the storage needs of the PSS and the transmission overheadneeded to pass bindings around. In some cases, the encoding method isfixed and known, so the encoding method identifier is not needed. Forexample, rather than transmitting and caching verbatim segments (i.e.,segments that literally represent substrings or subsequences of thetransaction data), the sending TA can transmit invertible functions ofthe segments, e.g., forward error correction encoded blocks of segments,encryptions of segments, signatures of segments, or the like. This wouldallow the receiving TA to decode different segments from a common poolof properly-encoded data, where if certain portions of the encoded datawere lost or corrupted, the original segments can still bereconstructed, thus adding error-correction to the link withoutrequiring changes at the clients or servers.

Other fields might be present in the PSS for tracking which segmentsmight be known by which recipients. In some implementations, the senderjust segments data and creates references independent of what thereceiver might be able to do with the results, but in otherimplementations, a sender maintains information usable to determinewhether a receiver might have a particular binding, such as by trackingwhich receivers previously received which segments. Storage for suchinformation could be optimized by recording which receiver(s) have whichsegment(s) in a Bloom filter (i.e., a bit vector indexed by the hash ofthe destination into the vector giving a rare false positive but nevergiving a false negative).

Some implementations might use a heuristic such that a server proxyincludes a segment binding only when it creates a new entry and otherclient proxies that need the segment will have to request it, as onlythe first client proxy will get the binding for the new segmentautomatically.

A TA might include routines for PSS housecleaning, such as a heuristicthat says to delete all segments in a client-side PSS related to aparticular file on a particular server when the client closes the file.The server-side PSS might also delete the corresponding segments, ordefer the housecleaning for those segments until all clients close thefile. Other housecleaning might involve deleting segment entries thathave exceeded their lifetimes or have not been used for a while. Otherheuristics might indicate when a particular segment binding is to beused and discarded.

The arrangement of the PSS has a number of benefits, some of whichshould be apparent upon reading this disclosure. Because segmentationcan occur at varying cut points and the segments can be independent ofthe transactions, the segments might survive in the PSS for arbitrarylengths of time and be used for transactions entirely unrelated to thetransaction in which the segment was created and stored. Because thesegment references are unique for unique segment data, a recipient canalways identify correctly the segment data for a segment reference (ifthe recipient has the segment). This is better than merely cachingresults. It is also an improvement over compression with localizedsignal statistics, such as building adaptive codebooks and the like.Segment names and content are independent of any particular bit stream,even if system components crash and reboot, new components are addedinto the mix, the persistent segment store is erased, etc. It should beunderstood that “persistent” as used to describe the PSS does not meanthat the segments are permanently stored and can therefore never bepurged; just that at least some of the segments persist at least beyondone transaction.

FIG. 4 illustrates an encoder 140 and a PSS 142. The TT for a TA mightbe just encoder 140, but the TT might also include other functionalityor elements. As shown, encoder 140 has an input for data to be encoded,and control inputs for encoding control parameters and out-of-bandinformation about the input data. Encoder 140 is shown with outputs forencoded data and segment bindings for storage in PSS 142. In operation,encoder 140 would process input data, identify segments of data, replacethe segment's data with a reference, provide the segment data and asegment reference to PSS 142 in the form of a binding, and output theencoded data. As shown in FIG. 4, the resulting encoded data mightcomprise references, bindings and residual data (such as data that couldnot be efficiently represented with references). Herein, a piece ofresidual data is also referred to as an “unreferenced segment”. In someembodiments, a distinction exists between data that is segmented but notreferenced and data which is not segmented. In the former, there is adefined segment beginning and end, but the segment contents are notreplaced with a segment reference, whereas in the latter, there mightnot be a segment beginning or end, as such. For simplicity of thefollowing description, the distinction is ignored.

Another output of encoder 140 is the segment bindings, for PSS 142 foruse in decoding incoming data (or for supplying to other TA's onrequest). Control inputs to encoder 140 might include a target segmentsize and out-of-band information might include parameters indicatingsuch things as the default lifetime of segments, information about thedata source, etc. The target segment size is a parameter that controlsthe average size of segments generated by the segmentation process. Ingeneral, segments vary in length with a certain distribution of sizes,and the target segment size controls the average such size generated bythe segmentation process. While segment size could be fixed, it ispreferable that the segment size be allowed to vary, so that segmentsmatch up more often than if the data handled by the system is segmentedinto arbitrary fixed segments.

The TT puts the bindings it creates in its own PSS for use in decoding,but also so that the “owner” of the binding (i.e., the TA that createdthe binding) can keep track of it, supply it to others and also refer toit when later data is encoded (so that segment references might bereused where the segment data repeats).

The TT⁻¹ of the owner of a binding will often re-use those bindings,such as when a sequence of segment data goes round trip, i.e., flowsfrom the STA to the CTA and back, or vice versa. This might happen, forexample, where a user edits a file. The user's file client will requestfile data, the server will serve the file and while the user edits thefile, the bindings for the file data will be present in both the CTA'sPSS and the STA's PSS. If the user writes back the file data, theportions that did not change may be fully represented by referencelabels created when the file data was first sent to the user's client.In this case, rather than create new bindings when sending data back tothe STA, the CTA simply references the old bindings that were created bythat same STA. Other examples include e-mail, where a client mightrequest an e-mail (via one protocol like IMAP or POP) and then forwardit back over the network (via another protocol like SMTP), in which casethe STA's TT⁻¹ can use bindings created by the STA's TT when the e-mailwas first sent to the client, presuming both SMTP transactions and IMAPor POP transactions flow through the STA/CTA pair. Another example iswhere a user copies information from a Web site (via HTTP) to a filesystem via CIFS, presuming both HTTP transactions and CIFS transactionflow through the STA/CTA pair.

Because of this characteristic of the PSS, a client and a server caneffectively send large blocks of data back and forth, using very littlebandwidth and without changing the client or the server. This isparticularly useful where large files are moved around and only changedslightly, such as where two or more users are collaborating on a largeCAD file. Using the systems shown here, network performance could besufficient to cause users to abandon other workarounds to networkbottlenecks, such as remote access, storing local copies of files,pushing out read-only copies of the files, etc.

If the input data is segmented according to content, the same sequenceof bits would likely result in the same segment, regardless of where thesequence of bits occurred. This has advantages, as repeated bitsequences are effectively noticed and referenced. However, where thereis a compelling need or improved performance, external factors mightcome into play. For example, some parameters about the transactionscould be used, possibly resulting in more than one segment being createdfor one sequence of bits, if there were an offsetting benefit. In oneapproach, an external factor is what segments exist in the PSS, andsegments boundaries are decided on based on what segments are alreadypresent in the PSS. While this is not as scalable as the more basicapproach described above, it might result in more reuse of segments andtherefore have some benefits.

This can be illustrated by an example. If a payload were normally cutone way, but a different set of cuts would more closely match segmentsthat are already in the PSS, greater compression would result. However,to be able to keep the gains, the sending TA would have to have someidea which segments the receiving TA probably has, so that the sendingTA does not make its cuts based on the sender's PSS if the sender knowsthat most of the sender's PSS segments are not present at the receiver'sPSS.

FIG. 5 illustrates a decoder 150 and a PSS 152. The TT⁻¹ for a TA mightbe just decoder 150, but the TT⁻¹ might also include other functionalityor elements. Decoder 150 receives encoded data, as might have beenoutput by decoder 140 shown in FIG. 4. As described above, the encodeddata might comprise references, bindings and residual data. When decoder150 encounters a binding in data it receives, it can use the segmentdata in that binding to reconstruct the original data and it can alsostore the binding in its PSS. When decoder 150 encounters a referencewithout a binding, it can use the reference to obtain segment data fromPSS 152 to reconstruct the segment. If the segment reference is notfound in PSS 152, decoder 150 can send a request for the segment data.

FIG. 6 is an illustration of an encoding process wherein input data issegmented and represented by references to data segments. As shownthere, the raw input data is loaded into a buffer 160 (although this canbe done without buffering, if necessary). The raw input data is thensegmented into segments. Several techniques are available fordetermining where to define the “cut lines” that separate each segmentfrom its adjacent neighbors. Some approaches to segmentation asdescribed in McCanne II. Other approaches that might be used are asimple approach of putting cut lines at regular intervals, or in somerelation to a fixed sequence of data found in the raw input data, suchas end-of-line marks, though such approaches might not lead to the bestperforming segmentation scheme.

However the cut lines are determined, in the example of FIG. 6, the rawinput data in buffer 160 is segmented into segments S_(A), S_(B), S_(C),S_(D), S_(E) and S_(F). In this example, the first five segments are tobe replaced with references and the references happen to be R₁₅, R₁₆,R₁₇, R₃ and R₈. Note that the references are not necessarily in order,and this example illustrates that some references (e.g., R₃ and R₈.)might be to segment data that was already encountered, in which case anew segment is not used, but the reference is to the preexistingsegment. Also illustrated here is that a segment (e.g., S_(F)) need notbe replaced with a reference.

The raw input data can be fully represented by the output data and thebindings, which can be generated from the raw input data. The bindingsare provided to the PSS for the TA that generated the bindings, as wellas others and some or all of the bindings might be sent as part of theoutput data. In this example, the new bindings are (R₁₅, S_(A)), (R₁₆,S_(B)) and (R₁₇, S_(C)). In this example, the bindings (R₃, S_(D)) and(R₈, S_(E)) are not needed because the segment data for segments S_(D)and S_(E) are already known and were stored with references to R₃ andR₈.

FIG. 7 is a flowchart illustrating a process for decoding data as mightbe output by the encoder of FIG. 4 and decoded by the decoder of FIG. 5.The steps of the process are labeled “S1, “S2”, etc., with the stepsgenerally proceeding in order unless otherwise indicated. In the firststep (S1) referenced data (e.g., data encoded with references) isreceived and parsed into tokens. If the token is checked (S2) and it isnot a reference, it must be an unreferenced segment and so the token isoutput directly (S3). However, if the token is a reference, the decoderchecks (S4) if the reference exists in the PSS supporting the decoder.If yes, the decoder gets the referenced segment from the PSS(S5). If no,the decoder sends a resolution request (S6) to the reference resolversupporting the decoder and receives the resolved referenced segment backfrom the reference resolver (S7). Where the reference label encodes thesource of the segment data, that label may be used by the referenceresolver to aid in finding the referenced segment.

Once the decoder has access to the referenced segment's segment data(either following step S3 or step S7), it outputs the segment data (S8).The decoder then checks for additional tokens (S9). If there are moretokens, the process repeats at step S2 with the next token, otherwisethe process completes.

The above description represents just one particular embodiment forencoding and decoding segment bindings and references using a PSS. Otherapproaches are possible that involve more sophisticated representationsof the relationships between labels and data, such as those shown inMcCanne II.

FIG. 8 is a block diagram of a networked system wherein transactionacceleration is implemented and uses a proactive segment distributor(“PSD”). As shown there, a PSD 210 includes a PSD controller 212, itsown PSS 214 and other storage 216 for PSD variables. In someimplementations, multiple PSD's are used, although only one is shown inthe figure.

By the operation of PSD 210, segments are more likely to be present whenthey are needed and therefore fewer segment resolution requests areneeded. Where the segments need to be moved from PSS to PSS, PSD 210 cantrigger this process in advance of the actual need for the segment, sothat a transaction will return more quickly, as the receiving TA doesnot have to block for the receiving TA to issue a request for a segmentto the sending TA as the payload is being received. PSD 210 can do thedistributing itself or just direct the owner (or other holder) ofsegments to pass them around. In some instances, PSD 210 might maintainits own PSS 214, but in some implementations, the PSD just directs theflow of bindings among PSS's and does not maintain its own PSS.

PSD 210 might monitor transaction flow from the CTA's 20 and STA's 22and from that, determine which segments are likely to be needed andwhere. When PSD 210 determines that a segment might be needed, it cansend a message to the sending TA, such as an STA serving a file systemor e-mail system. The message would direct the sending TA to performsegmentation, store bindings in its own PSS and even propagate thebindings to other PSS's, so that the segmentation is done when thesending TA receives a message that would result in the sending TAsending a payload. When done well, a receiving TA will obtain thebinding it needs for when the receiving TA receives a payload withreferences therein and those bindings can be sent when the bandwidth isnot so critical. More typically, the sending TA is an STA, but the PSDmight also direct CTA's to “pre-load” bindings into the system.

In some cases, server agents are added to servers to identify candidatesfor preloading. For example, a mail server such as a Microsoft Exchange™server might be coupled to a network and operate with an STA and anassociated server agent. The server agent would detect when e-mails andattachments arrive and, based on past observations or operator policies,pre-load a particular CTA with the relevant segment data. This might bedone by tracking which users read their emails from which locations,either through static configuration or preferably with measurements.Then, when a remote user goes to read e-mail, the bulk of the email datais already at the user's remote site, but the transactions still go backthe Exchange mail server to ensure protocol correctness.

In addition to proactively triggering segment generation, PSD 210 mightalso assist with “pre-populating” various TA PSS's with bindings thatalready exist so that those TA's have segment data ready when areference is received. In one implementation, PSD 210 operates on apropagation model, as is done with USENET news items, where new bindingsare noticed to PSD 210 and PSD 210 then propagates the new bindings fromthe noticing TA to all or some of the other TA's, which might in turnpropagate bindings. In lieu of, or in addition to the pre-populatingtriggered by the PSD, a sending TA might anticipate which segments needto be transmitted to a receiving TA and send them either ahead of timeor “out-of-band”) such that the receiving TA need not issue additionalrequests to resolve unknown segments.

Where indiscriminate propagation would likely lead to network overloador increased bandwidth usage relative to just sending complete, raw datafor each transaction, more sophisticated approaches might be used. In anexample of a more efficient approach, the PSD uses heuristics todetermine which TA's might need which segments. In another approach,servers include server agents that provide the PSD with information at ahigh level that allows the PSD to determine which CTA's will need whichsegments from the “agented” server. In some embodiments, combinations ofthe above approaches are used.

Another embodiment of a PSD with a server agent involves a type of filesystem mirroring. Here, the server agent monitors file system activityand whenever new data is written to the file system, the agent instructsthe PSD to replicate the appropriate segment bindings to one or moreCTA's. User- or operator-defined policies could dictate whether theentire file system's data is replicated or just configured portions arereplicated. Moreover, these policies could be augmented by measurementsof access patterns, so that segment data from the most frequentlyaccessed portions of the file system are replicated (and thesemeasurements could be performed on a per-CTA basis). As a result, eachsuch CTA effectively contains a mirror of all (or portions) of the filesystem data. Then, when clients interact with the CTA via networkfile-system protocols (like CIFS or NFS), the transactions flow all theway back to the origin file server, yet these transactions are whollycompressed into pure strings of references. This approach ensures thatthe original file system semantics are preserved as if all clients weresharing a single file server, yet the performance of the client-servercommunication behaves as if all data were in local per-client fileservers.

While the segmentation scheme outlined above can significantly reducethe bandwidth requirements of client-server communication, thetransactions are still subject to the inherent latency of communicationsacross the wide area. These latency bottlenecks can adversely impactperformance and can be dealt with using complementary techniques likefile read-ahead and write-behind. Because of the compression and stagingof data, however, read-ahead and write-behind techniques becomeextremely effective as they incur very little overhead on the networksince all the data is already present at the CTA.

All of these approaches can be complemented with a scheme to employbandwidth policies to the various sorts of CTA/STA communication. Forexample, a certain bandwidth limit could be imposed on the PSD to limitthe aggressiveness of the staging algorithms. In another example,bandwidth priorities could be applied to different classes of stageddata (e.g., file system segment replication could have priority overemail attachment segment replication).

FIG. 9 is a block diagram of a networked peer-to-peer system accordingto embodiments of the present invention. As shown there, various peers180 interact with each other via peer transaction accelerators (PTA's)182. Peers 180 might interact directly, although such connections arenot shown. In operation, one peer 180 might request data from anotherpeer, via each peer's PTA 182 and network 184. As shown, each PTA 182might comprise a peer proxy 190, a TT 192, a TT⁻¹ 194, a PSS 196 and anRR 198. In a peer to peer system, a peer is essentially functioning as aclient for some transactions and a server for other transactions, and sothe transaction acceleration scheme would function in an analogousmanner.

FIG. 10 is a block diagram of a networked system wherein transactionacceleration is implemented and the client-side transaction acceleratoris integrated in with the client as opposed to being a separate entity.As shown, a client system 302 is coupled through a network 304 to aserver 306 directly and a server 308 via a server transactionaccelerator STA 310. Client system 302 is shown including communicatingprocesses 320, a direct network I/O process 322, a CTA process 324, andstorage 326 including a persistent segment store 328. Communicatingprocesses 320 are coupled with direct network I/O process 322, CTAprocess 324 and storage 326. CTA process 324 is coupled to PSS 328.

In operation, communicating processes 320 perform functions, typicallyat the application layer, that require interaction with servers outsideclient system 302. For example, communicating processes might comprise aweb browser, an e-mail client, a Java program, and interactive networkprogram, a chat program, an FTP program, etc. Where a communicatingprocess is to interact with a server directly, the communicating processwill interact with direct network I/O process 322 to interact with aserver, but where the transaction is to be accelerated, thecommunicating process would interact with CTA 324. In some embodiments,a communicating process 320 and a CTA 324 may be components of a singleapplication program, while in other embodiments they may be separateapplication processes. CTA process 324 can accelerate transactions muchlike the various stand-alone CTA's do as described above, using aportion of storage 326 as the PSS. In some variations, PSS 328 isdistinct memory from storage 326, which is used for other processes inclient system 302, such as the needs of the communicating processes 320.

Direct network I/O process 322 satisfies the network I/O needs ofcommunicating processes 302 by interacting with servers over network304. In some cases, direct network I/O process 322 interacts with thesame servers as CTA 324, illustrated by the dotted line to server 308.Client system 302 might include other processes not shown, includingprocesses related to transaction acceleration. For example,communicating processes 320 might rely on a separate process thatdetermines when to send a transaction directly to a server and when toattempt to accelerate it.

FIG. 11 is a block diagram of a networked system wherein transactionacceleration is implemented and the server-side transaction acceleratoris integrated in with the server. That figures shows a server system352, a network 354, a client 356, a client 358 and a client transactionaccelerator (CTA) 360. Server system 352 is shown includingcommunicating processes 370, a direct network I/O process 372, an STAprocess 374, and storage 376 including a persistent segment store 378.Communicating processes 370 are coupled with direct network I/O process372, STA process 374 and storage 376. STA process 374 is coupled to PSS378. Client 356 couples to a server system 352 directly as illustratedby the line from client 356 to direct network I/O process 372, whichhandles transactions that do not go through STA process 374. Client 358couples to server system 352 via CTA 360 and STA process 374, but mightalso connect directly to direct network I/O process 374 for othertransactions.

In operation, communicating processes 370 perform functions such asserver processes that respond to requests from clients. Where serversystem 352 and a client are interacting directly, the transaction wouldflow between the communicating process and the client via direct networkI/O process 372. Where server system 352 and a client are interactingvia the TA's, the transaction would flow between the communicatingprocess and the client via STA process 374. STA process 374 canaccelerate transactions much like the various stand-alone STA'sdescribed above, using a portion of storage 376 as the PSS. In somevariations, PSS 378 is distinct memory from storage 376, which is usedfor other processes in server system 352, such as the needs of thecommunicating processes 370.

Direct network I/O process 372 satisfies the network I/O needs ofcommunicating processes 352 by interacting with servers over network354. In some cases, direct network I/O process 372 interacts with thesame servers as STA 374, illustrated by the dotted line to client 358.Server system 352 might include other processes not shown, includingprocesses related to transaction acceleration. For example,communicating processes 370 might rely on a separate process thatdetermines when to send a transaction directly to a server and when toattempt to accelerate it.

It should be understood that the elements of FIGS. 10 and 11 could becombined, such that client systems with internal CTA's can communicatewith server systems with internal STA'S. It should also be understoodthat where single arrowed lines are used, bi-directional information ordata flows might also be present.

One disadvantage of embedding the TA in the client and/or server devicesis that each device ends up with its own PSS and the benefits of cachingthe same segment data on behalf of a large number of clients (orservers) at a given location are diminished. This problem, however, canbe overcome in another embodiment that allows the PSS to logically spanmultiple TA's, preferably situated on a common LAN segment (or a commonnetwork area that is interconnected with high-speed links, e.g., ahigh-speed campus-area network that interconnects multiple floors in abuilding or multiple buildings in close proximity). In this case, thelogical shared PSS can either be another device attached to the networkor it can be several PSS's embedded in each CTA such that throughcooperative protocols (e.g., over IP Multicast) these PSS's behave as asingle, logical entity.

FIG. 12 is a block diagram of a networked system wherein transactionacceleration is implemented and a PSS is shared among a plurality oftransaction accelerators. As shown there, clients couple to a local CTA402 for transaction acceleration. Instead of maintaining a separate PSS,the local CTA's 402 are coupled to a shared PSS 404. Preferably, theconnection between the local CTA's and the shared PSS are higherperformance connections relative to the connections via network 405 thatwould exist between the client and the server. A shared referenceresolver 406 might also be present and coupled to the shared PSS 404 andthe local CTA's sharing that PSS.

When each local CTA 402 initiates a transaction with a request messageor receives a response message, that local CTA 402 would use shared PSS404 for storage and retrieval of segment data. This has an advantageover a system using separate PSS's for each local CTA, in that a segmentthat is stored as a result of a transaction for one local CTA could beused in a transaction for another local CTA. For example, if local CTA402(1) recently handled a transaction for a client that involved gettinga data from server S, the segments that server S created for thattransaction would likely exist in shared PSS 404. If local CTA 402(2)were to then handle a transaction for a different client (or the sameclient in some configurations, such as a round-robin local CTA sharingscheme) directed at server S, local CTA 402(2) would send the request tothe STA for server S. If the segments for the second transaction matchthose of the earlier transaction with local CTA 402(1), whether theyrepresent in fact the same request or an unrelated request where theresulting payload data has some data in common, local CTA 402(2) wouldreceive references to those segments instead of the segment data itself.

When a local CTA receives references to segments that cannot be resolvedfrom shared PSS 404, the local CTA can send a request for resolution toshared reference resolver 406. In some embodiments, each local CTA hasits own shared reference resolver that communicates its referenceresolutions to the shared PSS 404 as well as to other components of thelocal CTA of which it is a component. Other embodiments may employ asingle shared reference resolver used by all clients.

While a shared PSS is described in FIG. 12 as being on the client side,a similar arrangement can be made at the server side, either with sharedor individual PSS's on the client sides. Also, TA's with shared PSS'smight exist on the same networks as TA's with individual PSS's. AlthoughFIG. 12 shows shared PSS 404 as being distinct from the local CTA's, itmay be that the shared PSS is contained within one of the local CTA's,although it is external to other CTA's which share that PSS.

The PSS might be connected among the local CTA's it serves usinglocalized network multicast communication. In this approach, eachtransaction accelerator subscribes to a well-known and locally scopedmulticast group. By using localized scoping, the system can guaranteethat only transaction accelerators that are connected by a localhigh-speed network coordinate with one another through this mechanism.Each host can generate periodic session message packets sent to thisgroup (or another configured group for exchanging session packets),allowing the computation of a round-trip time estimation to othertransaction accelerators subscribing to that group. Well-knowntechniques could be used for this process, such as those shown in Floyd,S., et al., “A Reliable Multicast Framework for Light-weight Sessionsand Application Level Framing”, in IEEE/ACM Transactions on Networking,December 1997, Volume 5, Number 6, pp. 784-803 (hereinafter “Floyd etal.”). The session protocol allows all the members in the group to learnof each other's existence and can also infer the size of the group fromthe sum of members.

Using this multicast configuration, the system for caching segment datacan be enhanced in a number of ways. In one approach, whenever atransaction accelerator receives a new segment binding, it can multicastthat segment binding to all other transaction accelerators in thelocally scoped group. This can mitigate the problems outlined above witheach client having a separate PSS, as each PSS in the local set oftransaction accelerators would be replicas of each other and any givendata segment would thus be sent just once over the WAN connection.

To ensure the reliability of transmission over the network multicastconnection, a number of well-known schemes for reliable multicasttransport can be employed as in Floyd et al. and papers cited there-inon reliable multicast protocols. Given that this multicast communicationis conducted in a homogenous, high-speed local-area or campus-areanetwork, the difficult problems of congestion control and WAN multicastare altogether avoided.

FIG. 13 is a block diagram showing a multicast implementation of thesystem of FIG. 12, wherein multicast communications are used forupdating and reading a shared PSS. As with the arrangement shown in FIG.12, local CTA's 412 connect to clients and to network 405 and share ashared PSS 414 with other local CTA's. A shared RR 416 is configured tobe on the same multicast group 417 as each instance of shared PSS 414(indicated as 414(1), 414(2), . . . ). Logically, it might be said thatthe multicast group contains shared RR 416 and the local CTA's, if thelocal CTA's handle the I/O needed to read and write the shared PSS. Themulticast traffic is illustrated by the lines 418 in the figure.

In another approach, the PSS is not pro-actively replicated as describedabove, but rather a transaction accelerator can issue local requests toresolve unknown segments. That is, when a transaction acceleratorreceives a reference for data that it is not in its PSS, it transmits aresolution request message over the locally-scoped multicast group. Allof the other local transaction accelerators will thus receive therequest message, unless errors occur. A receiver that has the requesteddata in its PSS can then respond with the data. By using well-knownslotting and damping techniques (as in Floyd et al.), just one responsemessage typically will be transmitted over the network while incurringlittle delay.

If no response is received by the requestor (after some deliberate delaycomputed from the session message round-trip times), the requestorassumes that the data is not present in the local environment andtransmits the resolution request over the WAN to the transactionaccelerator that originally generated the data reference in question.Note that since the local round-trip time is comparatively small(typically less than 1 ms) compared to the WAN round-trip time(typically tens of milliseconds or more), the extra delay incurred bythis initial check is negligible (i.e., typically under a few percent),while the benefit is substantial due to the higher local networkperformance.

In yet another approach, a hybrid between the two approaches describedabove eliminates the delay associated with the local resolution request.In this hybrid approach, whenever a transaction accelerator receives anew segment binding, instead of multicasting the entire segment, itsimply multicasts the name of the segment. This way, all the localtransaction accelerators learn about what segments are present withoutnecessarily having to hold a copy of all the segment data. Then, when areference is received for a segment that is not in the PSS but whosename is recorded as locally known, the transaction accelerator can senda local request for the data and that local request can go directly tothe transaction accelerator that sent out the new segment binding if thesender can be identified. Otherwise, the accelerator can assume the datais not locally present and immediately send a request across the WAN.Even when the segment is inferred to be locally present, it is possiblethat it has been flushed from all the other local accelerators' PSS's.In this case, the requesting accelerator will still time out and revertto transmitting its resolution request across the WAN.

In yet another approach, the segment data stored across the PSS's of thelocal accelerator group need not be fully replicated. Here, eachaccelerator is responsible for a portion of the segment cache usingcooperative caching techniques. As described above, when a reference forsegment data managed by another accelerator needs to be resolved, therequest can be sent either directly to that device or indirectly overthe multicast group. Once the data has been reassembled and delivered tothe client (or server), it can be discarded and need not be entered intothe local PSS (since that segment data is being actively managed by theother transaction accelerator).

FIG. 14 shows a plurality of clients 502, with integrated CTA's. Clients502 are coupled to a LAN 504, which in turn couples clients 502 to a WAN506 via a LAN-WAN link 508. Not all clients on LAN 504 need include aCTA 512, but at least two clients are shown including integrated CTA's512. Each CTA is shown including a PSS 514 and an RR 514. With thisimplementation, all of the functionality of the CTA can be implementedas software running on the client.

A client's CTA 512 handles the acceleration of transactions requested bythe client applications 510 running on that client. For example, wherean application running on client 502(2) initiates a transaction with aserver that is to be accelerated, the connection would be to CTA 512(2).CTA 512(2) would then open a connection with a corresponding STA, muchas described above, over LAN 504 and WAN 506. When CTA 512(2) receives aresponse message including a payload that has been accelerated, CTA512(2) will use the contents of PSS 514(2) to deference the referencelabels in the accelerated payload.

To achieve the benefit of segments that might have been between serversand other clients on LAN 504, the PSS's 514 can be cooperative PSS's. Bycooperating, each CTA is able to use the segment bindings from its ownPSS as well as the PSS's of other CTA's on LAN 504. Then, if a segmentbinding cannot be found locally, a CTA's RR can send a request for thebinding over the WAN to the STA.

In some cases, when an RR receives a new binding (or its CTA createsone), it distributes the new binding to each of the other RR's on theLAN, so that each client's PSS is populated with the available bindingscreated on the LAN and a CTA will already have a copy of each of thebindings that are available on the LAN when the CTA is deferencingpayloads. This is referred to herein as “prescriptive cooperation”.

In other cases, the bindings are not distributed ahead of time, but aresent upon request. Thus, when an RR needs a binding it does not have, itmakes a request of the other RR's on the LAN for the binding. This isreferred to herein as “on-demand cooperation”.

In a hybrid of these approaches, when an RR receives a new binding orits CTA creates one, it distributes a “binding notice” indicating thenew segment's reference and the originating CTA to other CTA's on theLAN. When another CTA determines that it does not have a needed bindingin its own PSS, that CTA's RR checks a list of previously receivedbinding notices. If the needed binding is on the list, the requesting RRmessages the originator CTA to obtain the binding. If the RR determinesthat it does not have the binding and does not have a binding noticefrom another CTA on the LAN, the RR sends a request for the binding overthe WAN. This is referred to herein as “notice cooperation”.

It should be understood that a given LAN can implement more than one ofthe above-described cooperation schemes. The messaging among RR's forcooperation can be done using multicasting. For example, each of thecooperating clients (or their CTA's or RR's) can be a member of amulticast group. For prescriptive cooperation, each originating CTAmulticasts the new bindings it receives or creates. For on-demandcooperation, the requesting RR can multicast the request and theresponding CTA(s) can unicast or multicast their answers. Multicastingtheir answers allows the other CTA that did not request the binding toreceive it and possibly store it in that other CTA's PSS. For noticecooperation, the notices can be multicast, but for requests, those canbe unicast because the requester will know which CTA has the requestedbinding. Of course, a notice cooperation system could be implementedwhere the binding notices do not indicate the origination CTA, or thatinformation is not stored, in which case the binding request might bemulticast, but the preferred approach when using notice cooperation isto keep track of which CTA sends which notice.

FIG. 15 a block diagram of a networked system wherein transactionacceleration is implemented and the network handles a variety ofprotocols and services. The CTA and STA are shown coupled to accelerateCIFS, NFS, SMTP, IMAP and HTTP transactions. In other arrangements, theservers are at varied locations and the clients are at varied locations.In each case, the transactions for the accelerated protocols passthrough the CTA and the STA and can be accelerated as described aboveand be transparent to the clients and servers engaging in thetransactions. In addition to the open protocols illustrated in thefigure, the CTA's and STA's can accelerate transactions for proprietaryprotocols such as Microsoft Exchange™, Lotus Notes™, etc. As with othervariations described herein, the TA's might be integrated in with theclients and servers. For example, some software vendors might includetransaction acceleration as part of their client-server software suite.

The above description is illustrative and not restrictive. Manyvariations of the invention will become apparent to those of skill inthe art upon review of this disclosure. The scope of the inventionshould, therefore, be determined not with reference to the abovedescription, but instead should be determined with reference to theappended claims along with their full scope of equivalents.

1. In a network wherein clients initiate transactions with servers andthe network carries request messages from the clients to the servers andresponse messages from the servers to the client and wherein at leastone of the request messages and the response messages contains a payloadto be transported over the network from a sender to a receiver, a methodof accelerating transactions comprising: segmenting the payload intozero or more segments and zero or more symbols of unsegmented data; foreach of the segments, determining whether to send the segment data inthe payload as an unreferenced segment or as a referenced segment; foreach of the referenced segments, replacing at least some of the segmentdata with a reference to the replaced data and storing the replacedreference data associated with its reference; sending the payload fromthe sender to the receiver as an accelerated payload comprising zero ormore segment references and zero or more symbols of unreferenced data;receiving the accelerated payload over the network; identifying the zeroor more segment references in the accelerated payload; replacing the oneor more segment references in the accelerated payload with segment dataavailable to the receiver, to form a reconstructed payload; andproviding the reconstructed payload to the receiver as the transportedpayload.
 2. The method of claim 1, further comprising: deploying two ormore transaction accelerators in a network; receiving the payload from asender server or sender client at a first transaction accelerator;sending the accelerated payload from the first transaction acceleratorto a second transaction accelerator; and sending the reconstructedpayload from a second transaction accelerator to the receiving client orreceiving server, such that the acceleration is transparent to thesender's sending protocol and to the receivers' receiving protocol. 3.The method of claim 1, further comprising: determining, at thetransaction accelerator associated with the receiver, when segment datafor a referenced segment is not available for payload reconstruction;and requesting segment data from a transaction accelerator associatedwith the sender.
 4. The method of claim 1, further comprising: whensegment data is to be stored as part of a segment reference,transforming the segment data via an invertible function of the segmentdata, and storing the results of this transformation; and when segmentdata is to be used in dereferencing a segment, untransforming the storedresults using an inverse of the invertible function.
 5. The method ofclaim 4, wherein the invertible function is one or more of a forwarderror correction function, an encryption function and a signaturefunction.
 6. In a network wherein clients initiate transactions withservers and the network carries request messages from the clients to theservers and response messages from the servers to the client and whereinat least one of the request messages and the response messages containsa payload to be transported over the network from a sender to areceiver, a transaction accelerator comprising: a transactiontransformer for transforming a payload of a message to be sent,comprising: a) a segmenter for segmenting the payload into zero or moresegments and zero or more symbols of unsegmented data; and b) a replacerfor determining whether to represent the segment data of each segment asan unreferenced segment or as a referenced segment; a persistent segmentstore that stores segment data and segment references for referencedsegments; an inverse transaction transformer for untransforming anaccelerated payload from a transaction transformer of a remotetransaction accelerator, comprising: a) a tokenizer that determineswhere segment references appear in the accelerator payload; and b) adereferencer for substituting segment data from the persistent segmentstore for each segment reference detected by the tokenizer; a referenceresolver for resolving references as needed by the dereferencer whenencountering a segment reference to a segment that is not present in thepersistent segment store.
 7. In a network wherein clients initiatetransactions with servers and the network carries a request message froma client to a server and a response message from the server to theclient and wherein at least one of the request message and the responsemessage contains a payload to be transported over the network from asender to a receiver, an improvement comprising: a client-sidetransaction accelerator, comprising: a) a proxy coupled to the clientfor receiving request messages for delivery to servers and for relatingreconstructed response messages from the servers to the client; b) atransaction transformer for transforming a request message received fromthe proxy, comprising: i) a segmenter for segmenting the request messagepayload into zero or more segments and zero or more symbols ofunsegmented data; and ii) a replacer for determining whether torepresent the segment data of each segment as an unreferenced segment oras a referenced segment; c) a persistent segment store that storessegment data and segment references for referenced segments of therequest message payload, wherein segments with distinct segment datahave distinct segment references and the distinct segment references canbe independent of the transaction in which the segment reference wascreated; and d) an inverse transaction transformer for untransforming aresponse message payload into a reconstructed response message when theresponse message has been accelerated, comprising: i) a tokenizer thatdetermines where segment references appear in the response messagepayload; and ii) a dereferencer for substituting segment data from thepersistent segment store for each segment reference detected by thetokenizer; and a server-side transaction accelerator, comprising: a) aproxy coupled to the server for receiving response messages for deliveryto clients and for relaying reconstructed request messages from clientsto the server; b) a transaction transformer for transforming a responsemessage received from the proxy, comprising: i) a segmenter forsegmenting the response message payload into zero or more segments andzero or more symbols of unsegmented data; and ii) a replacer fordetermining whether to represent the segment data of each segment as anunreferenced segment or as a referenced segment; c) a persistent segmentstore that stores segment data and segment references for referencedsegments of the response message payload, wherein segments with distinctsegment data have distinct segment references and the distinct segmentreferences can be independent of the transaction in which the segmentreference was created; and d) an inverse transaction transformer foruntransforming a request message payload into a reconstructed requestmessage when the request message has been accelerated, comprising: i) atokenizer that determines where segment references appear in the requestmessage payload; and ii) a dereferencer for substituting segment datafrom the persistent segment store for each segment reference detected bythe tokenizer, wherein at least one segment in either the requestmessage payload or a response message payload is sent as a referencedsegment.
 8. The improvement of claim 7, further comprising: aclient-side reference resolver for resolving references as needed by theclient-side dereferencer when encountering a segment reference to asegment that is not present in the client-side persistent segment store;and a server-side reference resolver for resolving references as neededby the server-side dereferencer when encountering a segment reference toa segment that is not present in the server-side persistent segmentstore.
 9. The improvement of claim 7, wherein one of the client-sidetransaction accelerator and the server-side transaction accelerator is afirst transaction accelerator and the other one of the client-sidetransaction accelerator and the server-side transaction accelerator is asecond transaction accelerator, the improvement further comprising:means at the first transaction accelerator for anticipating segmentrequirements of the second transaction accelerator; and means forconveying anticipated segments from the first transaction accelerator tothe persistent segment store of the second transaction accelerator priorto the need of those anticipated segments by the dereferencer of thesecond transaction accelerator.
 10. The improvement of claim 7, furthercomprising: means, at each transaction accelerator of a set oftransaction accelerators cooperating over a network, for allocatingsegment reference identifiers such that the segment referenceidentifiers are unique over the set of transaction accelerators, whereinthe segment reference identifiers are selected from an effectivelyunbounded identifier space; and means for compressing the segmentidentifiers to form compressed segment identifiers used in one or moreof data storage and data transmission.